1. Field of the Invention
The present invention relates to an electrical chemical plating process, and more particularly, to an electrical chemical plating process having a pre-electrical-plating step so as to enhance the bottom filling ability of the metal layer.
2. Description of the Prior Art
As transistor devices continue to shrink in modern technology so do the feature sizes of the metal interconnection systems, and conventional metal material used as the metal interconnection systems is no longer suitable in current semiconductor industry because of its poor gap filling ability. Accordingly, metal copper which has high conductivity and good gap filling ability is widely used to manufacture metal interconnects having low critical dimension.
A chemical vapor deposition process is usually used to form a copper layer in conventional arts. The chemical vapor deposition process uses organic compounds as the source gas, so the resistively of formed copper layer is usually higher, especially when the thickness of the copper layer is increased. In addition, the residue after the CVP will result in poor adhesion between the copper layer and the above layer. Moreover, the cost of the CVP is usually high and is not suitable for semiconductor manufacturing processes.
Currently, a technology called electrical chemical plating (ECP) is widely used in the industry to form the copper layer, which can streamline the cost and form copper layers with low resistively. In the ECP process, a semiconductor substrate is immersed into an electrolytic solution containing copper ions. When a voltage is supplied, the copper ions will be reduced to form metal copper on the semiconductor substrate. However, conventional ECP processes usually confront a problem of poor bottom up filling rate, which may result in voids in the formed copper layer and therefore decrease the quality of the products. Accordingly, a lot of ECP processes are studied to provide a copper layer with good gap filling ability.